1. Field of the Invention
The present invention relates heat exchangers and more particularly to a device for reducing the thermal stresses in the bottom of a vertical heat exchanger between a primary liquid alkali metal heated in a fast neutron nuclear reactor and a secondary liquid alkali metal, the device including an axial conduit for introduction of the secondary liquid alkali metal, surrounded by a bundle of tubes fixed on a tubular plate, the secondary liquid alkali metal circulating upwardly in the tubes of the bundle and the primary liquid alkali metal circulating downwardly around the tubes of the bundle, and a chamber for supplying the tubes of the bundle, disposed beneath the bundle and the supply conduit, and wherein the bottom of the vertical heat exchanger is surrounded by an envelope defining a space filled with primary liquid alkali metal.
2. Description of the Prior Art
In exchangers of this type, considerable differences in temperature in steady state and in transient state, in the course of starting up and changes in operation occur between the primary liquid alkali metal, generally sodium, leaving the heat exchange tubular bundle, and the secondary liquid alkali metal arriving at the inlet of the tubes of the tubular bundle. This temperature difference is capable of creating considerable thermal stresses in the wall of the lower bottom of the exchanger which may lead to deformations or ruptures.
It has already been proposed to overcome these temperature differences by providing the bottom of the exchanger with a thermal shield, a double wall surrounding the bottom of the exchanger and a shield of liquid alkali metal enclosed between the bottom and the double wall. Such a shield which is sufficiently effective to reduce the differences in temperature, and therefore the thermal stresses, in steady state, is much less so during transient fast states.